Ultrasound probe for use with transport catheter and method of making same

ABSTRACT

A probe for use within a catheter is disclosed. The probe transducer portion is constructed of a crystal hollow cylinder with an inside lead attached to the inner surface of the crystal cylinder. One end of the outside lead is positioned close to the outer surface, in a plane tangential to the outer surface, and is coupled to the outer surface of the crystal cylinder by a thin sputtered layer of conductive material. The probe transducer also includes a layer of acoustically absorbing material on the proximal end of the crystal, and layer of acoustically coupling material on the distal end of the crystal cylinder. The transducer element simultaneously generates an axially oriented signal beam at one frequency and a radially oriented signal beam at 2 different frequency. The signal beams are analyzed to calculate the blood flow area and the blood flow velocity, the product of which is the blood flow rate.

BACKGROUND OF THE INVENTION Related Application Data

This is a divisional of co-pending U.S. application Ser. No. 07/865,163filed on Apr. 8, 1992 and now abandoned, which is a continuation-in-partof commonly owned, co-pending application, Ser. No. 07/790,724, filed onNov. 8, 1991 and now U.S. Pat. No. 5,246,016.

FIELD OF THE INVENTION

The present invention relates to an improved ultrasound probe and methodof making an ultrasound probe for use in connection with a multi-lumentransport catheter. The present invention more particularly relates toan improved ultrasound probe that allows for more accurate ultrasoundreadings and has a relatively small outer diameter, such that it can beused in connection with an improved catheter which can accept variousprobes for sensing biological conditions and parameters and which allowshigh fluid flow rate for introducing fluids irrespective of the presenceof sensing instruments in the catheter, thereby reducing the risk ofpatient complications.

Description Of Related Art

Numerous catheters exist for sensing, diagnosing and treating variousbiologic conditions. For example, there are cardiac catheters used forangioplasty, for measuring cardiac output, such as thermodilutioncatheters, pulmonary artery wedge pressure monitors, blood flow monitorsand temperature monitors. In use, a transport catheter is initiallyintroduced into an appropriate vessel or body cavity. In the case of athermodilution catheter, for example, the transport catheter may beintroduced into an appropriate vein. Thereafter, the thermodilutioncatheter is inserted and passed through the right atrium and ventricleand out to the pulmonary artery. After the catheter is properlypositioned and the balloon inflated, various readings can be taken ofleft heart pressure, for example, and pulmonary artery temperature. Thesame measurements may be taken a number of times while the catheter isin place. However, if the patient's condition changes and requires othermeasurements or diagnosis, or additional information is desired, such asmay be required in view of the results obtained by the thermodilutionmeasurements, the thermodilution catheter must be removed andsubstituted with a different catheter for such measurements. Thesubsequent catheter exchange increases the possibility of infectionthrough the introduction of a second catheter and increases theprobability of other problems such as venous puncture.

Another problem with frequent catheter exchange is that only physiciansare authorized to remove and replace catheters and probes in thepatient's body. However, after a physician has inserted and positionedthe catheter in the patient's body, a trained nurse is permitted toinsert, position, and replace probes within the catheter, since theprobe does exit the catheter. Therefore, it is desirable to use atransport catheter in connection with a probe, such that the probe canbe used within the transport catheter without the removal andreplacement of the transport catheter.

In the past, multi-lumen catheters were designed wherein the catheterbody was divided into circular sections of similar size or substantiallytriangular sections to form the separate lumens. These catheters weregenerally too small to accept sensing probes and one or more of thelumens of such catheters occasionally become constricted at the seal ofthe transport catheter. A further disadvantage of these multi-lumencatheters becomes apparent if an ultrasound probe was to be used withinone of the lumens of the catheter in order to obtain diagnosticreadings. In this case, the similar sized lumens surrounding theprobe-carrying lumen contain relatively large amounts of air space thatcause undesirable attenuation of the ultrasonic signal.

Undesirable signal attenuation is also caused by the transducer designof the prior art ultrasound probes. For example, ultrasound probetransducers may be formed of crystal material, having two leads attachedto the crystal material. The first lead is connected to the innersurface of the crystal material, and the second lead is connected to theouter surface of the crystal material. The location of the second leadon the crystal material causes a "dead" spot in the attenuation patternof the ultrasound signal. Therefore, the ultrasound probe does notprovide as accurate of a reading as desired. Also, the attachment of thesecond lead to the outer surface of the crystal cylinder causes theouter diameter of the ultrasound probe to increase, making it difficultto fit the ultrasound probe within the transport catheter. Therefore, aneed exists for an ultrasound probe having a relatively small outerdiameter, and which does not produce dead spots in the attenuationpattern of the ultrasound signal.

In patients undergoing major surgery or suffering from serious illness,there is an acute need for a continuous blood flow measurement, ascompared to an intermittent blood flow measurement. Therefore,ultrasonic transducer probes have been designed to continuously measurecardiac blood flow.

A known method of calculating blood flow is to multiply the area of theblood flow times the velocity of the flow. Methods have been developedfor using ultrasound transducers to calculate the area and to calculatethe blood flow velocity. For example, it is known to use echo patternsto determine the cross-sectional area of a blood vessel, and to use aDoppler technique to determine blood flow velocity.

However, in order to measure both cross-sectional area and velocity, twoseparate and distinct ultrasound transducer elements were used. A firsttransducer element was used to obtain measurements of the flow area, anda second transducer element was used to obtain measurements of the flowvelocity. For example, in one method, several transducer elements arelocated at the catheter tip. A first plurality of transducer elementsare activated and used to calculate the cross-sectional area of thevessel perpendicular to the catheter tip by echo methods. With the samecatheter, a second distinct annular transducer element is activated todetermine the velocity of the blood which flows perpendicular to thecross-sectional area. The velocity is determined by using the Dopplerprinciple, wherein the Doppler shift created by the movement of theblood cells is analyzed. The product of the two measurements providesthe blood flow measurement.

Another method of determining blood flow includes a method wherein thetransducer generates a single large uniform cone-shaped beam whichextends forwardly into the pulmonary artery. However, in this method,only a single cone-shaped beam is analyzed, and a radially-oriented beamis not utilized to determined the cross-sectional area of the artery.

With many of the known ultrasound probes, the probe must be axiallyaligned within the blood vessel and blood flow in order to provide anaccurate reading. If the probe is not properly aligned, the angle ofincidence between the probe axis and the blood flow adversely affectsthe accuracy of the ultrasound probe measurements. Therefore, a needexists for an ultrasound probe with a single transducer element that cangenerate a radially oriented signal beam and a forwardly oriented beamsimultaneously, and which is not affected by the angle between the axisof the transducer and the blood flow.

There is also a need for an improved catheter which can accept anultrasound probe, and which also, simultaneously, allows for high fluidflow for fluids to be introduced into the body, as well as theintroduction of relatively viscous fluids. Additionally, a need existsfor a multi-lumen catheter that minimizes the sizes of the lumens whichmight contain ultrasonic wave attenuating air in lumens adjacent aninstrument containing lumen.

SUMMARY OF THE INVENTION

One object of the present invention is to provide an ultrasound probethat provides increased accuracy in ultrasound readings by reducing deadspots in the sound wave attenuation pattern.

Another object of the present invention is to provide an ultrasoundprobe with a relatively small outer diameter.

A further object of the present invention is to provide an ultrasoundprobe that can be used in connection with a multi-lumen transportcatheter.

Another object of the present invention is to provide a transportcatheter that provides a plurality of lumens for accepting varioussequential probes through at least one of the lumens without requiringthe insertion and removal of a different catheter with each probe.

Yet another object of this invention is to provide a transport catheterwith a plurality of lumens that allows for an increased accuracy inultrasound readings by minimizing the attenuation of the signal causedby the quantity of air space in the surrounding lumens.

Still another object of this invention is to provide an ultrasound probewith a single transducer element that can generate a radially orientedsignal beam and a forwardly oriented beam substantially simultaneously.

Yet another object of the present invention is to provide an ultrasoundprobe with a single transducer element for measuring blood flow that isnot affected by the angle of incidence between the axis of thetransducer and the blood flow.

These and other objects are achieved through an ultrasound probe for usewithin a transport catheter, comprising a probe body having a distal anda proximal end, and a transducer portion attached to the probe bodydistal end. The transducer portion of the probe comprises apiezoelectric crystal in the form of a hollow cylinder having a distalend and a proximal end, and further defining an inner surface and anouter surface. An inside lead is coupled to the inner surface of thecrystal cylinder, and an outside lead is coupled to the outer surface ofthe crystal cylinder. The outside lead has a first and a second end,wherein the first end is coupled to the outer surface of the crystalcylinder by a conductive material, while a substantial portion of theoutside lead remains within the diameter defined by the crystalcylinder. The preferred transducer portion includes a layer ofacoustically coupling material deposited adjacent the distal end of thecrystal and a layer of acoustically absorbing material depositedadjacent the proximal end of the crystal cylinder.

The transducer portion alternately generates a radially oriented signalbeam at a first frequency, and then generates a forwardly orientedsignal beam at a second frequency. The signal beams are used tocalculate cross-sectional area and blood flow velocity, respectively,which are then used to calculate blood flow.

The probe is preferably designed for use within a catheter of thepresent invention comprising a catheter body having an outer edge withan outer dimension and having a proximal end and a distal end. The bodyalso includes walls defining, in transverse cross-section, a pluralityof lumens extending longitudinally substantially through the catheterbody including a first wall defining a first lumen having a firsttransverse dimension approximating about half of the dimension of thecatheter body. A second wall defines a curved lumen wherein the lumenoccupies at least a quarter of an arc around the catheter body.

The above described objects and other objects of the present inventionwill now become apparent from a review of the drawings and the followingdescription of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the transport catheter of the presentinvention.

FIG. 2 is a cross-sectional view of the transport catheter of thepresent invention taken along line 2--2 of FIG.1.

FIG. 3 is a perspective view of a catheter according a furtherembodiment of the present invention showing a probe and an injectateport.

FIG. 4 is a transverse cross-sectional view of the catheter of FIG. 3taken along line 4--4.

FIG. 5 is a longitudinal cross-sectional view of a portion of thecatheter of FIG. 3.

FIG. 6 is a partial segmented side-sectional view of a catheteraccording to a further embodiment of the present invention.

FIG. 7 is partial segmented side-sectional view of an ultrasound probeof the present invention.

FIG. 8 is a side-sectional view of a transducer of the ultrasound probeof the present invention.

FIG. 9 is a representational view of the ultrasound probe with a singletransducer element generating radially and forwardly oriented signalbeams within a blood vessel.

FIG. 10 is a schematic representation of the signal source for theultrasound probe.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, a catheter 10 for accepting probes and forintroducing fluid through the catheter and into a body cavity is shownwhich allows numerous procedures to be done using a single catheter andwhich reduces the likelihood of injury to the patient. In one preferredembodiment, the catheter 10 is primarily comprised of a catheter body12, an inflation balloon 14, a plurality of extension tubes 16, and aplurality of threaded hubs 18. The catheter body 12 has a proximal end20 and a distal end 22. The inflation balloon 14 is mounted to thecatheter body 12 at the distal end 22 of the catheter body 12 as wouldbe known to one skilled in the art. Each of the extension tubes 16 has arespective first end 24, which is coupled to a corresponding one of aplurality of lumens (shown in FIG. 2) in the catheter body 12 at thecatheter body proximal end 20 at a backform 28. The extension tubes 16provide access to each of the respective lumens. The extension tubecorresponding to the first lumen, described more fully below, alsoincludes graduations on the outside of the tube to indicate the depth ofinsertion of any probe or instrument passed along the first lumen. Thesecond end 26 of each of the extension tubes 16 is coupled to arespective one of the plurality of threaded hubs 18. The threaded hubs18 each have a luer taper common in the art for connecting suitableinstruments, such as probe connectors, an inflation device for theinflation balloon and an injection device for the injectate lumendescribed more fully below.

Referring now to FIG. 2, a cross-sectional view of the catheter body 12is shown taken at an approximate mid-point of the catheter body. Aplurality of walls within the catheter body 12 define the respectiveplurality of lumens. A first wall 34 defines a first lumen or probelumen 36. The cross-sectional configuration of the probe lumen 36 ispreferably circular, and has a diameter in the preferred embodiment ofapproximately half the diameter of the cross-section of the catheterbody 12. A second wall 38 defines a second lumen or an injectate lumen40. In the preferred embodiment shown in FIG. 2, the cross-section ofthe injectate lumen 40 is crescent-shaped. A suitable size for thesecond lumen is one where it occupies at least a quarter of an arcaround the cross-section of the catheter body 12. A third wall 42defines a third, inflation lumen 44, in cross-section preferablycircular, and a fourth wall 46 defines a fourth lumen 48, alsopreferably circular.

The probe lumen has a large cross-sectional area and preferably occupiesa significant portion of the cross-sectional area of the catheter sothat the catheter can accept as many different types and configurationsof probe as possible and to permit a wide variety of tasks or procedureswithout having to remove the catheter. The probe lumen also accepts theimproved ultrasound probe of the present invention herein. The probelumen is also preferably large enough to permit fluid flow within thelumen even while a probe or other element is in the probe lumen. Thisallows simultaneous instrument sensing and pressure monitoring orintroduction of fluid such as pharmaceutical through the probe lumen,even with concurrent introduction or withdrawal of fluid through theinjectate lumen 40. In this manner, removal of the probe is not requiredbefore injectate can be introduced or blood withdrawn through the probelumen. Fluid pressure can also be monitored even while a probe is inplace in the lumen 36. For example, the lumen 36 is capable of acceptinghemoglobin oxygen saturation probes, pacing probes, cardiac outputprobes, right heart ejection fraction probes, right heart ejectionfraction with hemoglobin oxygen saturation probes, hemoglobin pH probes,and high fidelity pressure monitoring probes. A preferred probeconfiguration is circular in external dimension. In one preferred formof the invention having the four lumens as described, a 71/2 Frenchcatheter has a 0.056 inch diameter probe lumen and the probes arepreferably around 0.042 inches in diameter.

The advantage of the probe substitution feature of the probe lumen 36 isapparent from a description of the use of the catheter 10. In use, thecatheter body 12 is first inserted and properly positioned in the bodyby a physician. A selected probe is then inserted through the probelumen 36 of the catheter body 12, by either a physician or a nurse, andthe desired procedure is carried out. Thereafter, another type of probemeasurement may be required such as where the patient's conditionchanges. The first probe is then removed from the catheter body 12,leaving the catheter body 12 in place, and a second probe is insertedthrough the probe lumen 36 of the catheter body 12 in order toaccomplish a different probe function. The insertion and removal of thecatheter body with each type of probe is avoided, and a nurse ispermitted to insert and remove each of the probes without requiring thephysician's presence. As a result, there is significantly less risk tothe patient of infection from the repeated insertion and removal ofcatheters, as well as less risk of venous puncture or other problems.Moreover, because the insertion and removal of the probes can beaccomplished by a nurse, the insertion and removal process of the probesis more convenient and efficient while the physician may otherwise beoccupied.

The large cross-sectional area of the injectate lumen 40 allows for ahigh fluid flow rate through the lumen, and also accommodates the flowof relatively viscous fluids. Therefore, the second lumen 40 iswell-suited for procedures requiring either high fluid flow rates or theintroduction of relatively viscous fluids. The second, injectate lumen40 is even more significant where fluid must be introduced or withdrawnat the same time the probe lumen is being used. The cross-section of theinjectate lumen 40 is preferably crescent-shaped, with the cross-sectionof the lumen covering or extending around at least a quarter arc of thecatheter body cross-section. The crescent shape allows for maximum fluidflow area within the catheter body 12 without interfering with the firstlumen 36.

The third lumen 44 is preferably used for inflating and deflating theinflation balloon 14 to properly position the catheter, for examplewhere the catheter is used as a thermodilution catheter. The fourthlumen 48 is preferably used for instrumentation, such as for passingthermistor wires or the like along the catheter to a point where asensing device is located in the catheter.

The catheter body 12 of the present invention is preferably formed byany of several well known extrusion methods. The catheter body 12 may befabricated from any of a variety of suitable materials, including, butnot limited to, flexible polyvinyl chloride (PVC), polyurethane, nylon,or polypropylene. The catheter body 12 is also preferably coated withheparin.

In the preferred embodiment described herein, the catheter body 12 hasan outer diameter of 0.101 inches centered on the central axis 50 of thecatheter. The total cross-sectional area of the catheter body 12 istherefore approximately 0.008 square inches. The first lumen 36preferably is circular with a diameter of 0.056 inches and includeswithin it the central axis 50. The cross-sectional area of the firstlumen 36 is therefore approximately 0.0024 square inches, which equatesto approximately thirty percent of the catheter body cross-sectionalarea. The cross-sectional area of the crescent-shaped second lumen 40 isapproximately 0.0016 square inches, which is approximately twentypercent of the total cross-sectional area of the catheter body 12. Thelargest distance between oppositely arcing surfaces in the crescentshape is about 0.024 inches and the radius of curvature of the ends ofthe injectate lumen is about 0.010 inches. To optimize the availablearea that can be used for fluid flow, the injectate lumen in thepreferred embodiment is symmetrically placed above the probe lumen andcentered so that an imaginary vertical plane (vertical when viewing FIG.2) through the central axis 50 and the central axis of the probe lumenbisects both the probe lumen and the injectate lumen. It should beunderstood, however, that where one or the other of the third or fourthlumens is omitted, the injectate lumen may be formed asymmetricallyrelative to a line through the central axis 50 and the central axis ofthe probe lumen. The third lumen 44 and the fourth lumen 48 are bothpreferably circular, and have a diameter of approximately 0.012 inches.Therefore, the cross-sectional areas of the third lumen 44 and thefourth lumen 48 are each approximately 0.0001 square inches, whichequates to approximately one and one-half percent of the totalcross-sectional area of the catheter body 12. The smallest dimensionfrom any of the lumens radially to the outer edge of the catheter bodyis preferably 0.007 inches. The thickness of any wall between lumens ispreferably at least 0.007 inches. The dimensions of the catheter body 12and lumens given are preferred, but they are exemplary only of thepreferred embodiment of the invention.

It should be understood that the cross-sectional configuration shown inFIG. 2 is preferred, and extends in the preferred embodimentsubstantially the entire length of the catheter. However, it should alsobe understood that the inflation lumen 48 terminates at the inflationballoon 14. It should also be understood that the injectate lumen mayopen at an injectate port 52 through the outer catheter wall at asuitable location near the distal end 22 along the length of thecatheter body (FIG. 3). Where the catheter has an overall usable lengthof 110 centimeters, the injectate port 52 is typically located about 30centimeters proximal of the distal end of the catheter, a standarddistance for a thermodilution catheter. A thermistor 54 is exposed tothe outside of the catheter approximately 4 centimeters proximal of thedistal end.

Considering the distal-most portions of the catheter in more detail(FIGS. 4 and 5), fluid flow out the injectate port is created by placingan injectate lumen plug 56 in the injectate lumen 40. The plug 56 has ageneral transverse cross-section conforming to that of the injectatelumen and is sealed in place by a suitable biocompatible filler. Thethermistor 54 is potted in an opening formed in the outer cathetersurface. Preferably, the thermistor is potted in the injectate lumensince the injectate lumen downstream of the plug 56 is otherwise unused.Thermistor wires 58 from the fourth lumen 48 pass into the injectatelumen 40 through a cross-over 60 from the fourth lumen.

In order to reduce the volume of air in the unused and therefore vacantportion of the injectate lumen, namely the portion of the injectatelumen distal of the plug 56, a crescent shaped insert or rod 62 isinserted in the injectate lumen and fixed with a suitable adhesive 64between the plug 56 and the cross-over 58. The rod is preferably formedfrom the same material as the catheter and preferably to provide thesame flexibility as the catheter without the plug. A probe 66 is shownin FIGS. 4 and 5 and can be made from plastic, metal, plastic coatedmetal, composites or other suitable materials used in manufacturingprobes, sensors or other instrumentation.

A hemostasis valve 67 is also shown in FIG. 3 through which the probepasses into the extension tube. An injection port may also be connectedto the valve 67 through an appropriate stopcock, shown schematically at67A, to which may be connected a conventional pressure sensor device, afluid injection device, and the like.

The orientation of the lumens within the catheter body 12 accommodatesthe four lumens with the probe and injectate lumens having a relativelylarge cross-sectional area. As a result, the cross-sectional areas ofthe third and fourth lumens remain relatively small. In use, the probeand injectate lumens are filled with a liquid, with only the third andfourth lumens containing any appreciable air space. The relatively smallquantity of air space in the third and fourth lumens minimizesundesirable attenuation of ultrasonic signals when an ultrasound probeis used within the probe lumen 36. Therefore, an ultrasound probe usedin the probe lumen of the preferred embodiment produces a more accurateresult.

The accuracy of the ultrasound probe readings within the transportcatheter is also increased when an ultrasound probe 82 of the presentinvention is used. The ultrasound probe 82 is shown in detail in FIG. 7.The use of the ultrasound probe 82 within the first probe lumen 36allows the nurse or physician to reposition the probe 82 until it isproperly positioned, without causing unnecessary tissue or vasculardamage. Moreover, as discussed above, the physician is not required toposition the probe within the transport catheter, because a nurse ispermitted to replace probes within the catheter. Therefore, theplacement of the probe within the catheter body allows for moreconvenient and less traumatizing replacement and repositioning of theprobe.

Referring now to FIG. 7, an ultrasound probe 82, according to one aspectof the present invention, comprises a probe body 84 having a proximalend 86 and a distal end 88, a connector 90, and a transducer portion 92.The connector 90 is coupled to the probe body proximal end 86, and thetransducer portion 92 is connected to the probe body distal end 88. Theconnector 90 is of the type known in the art for use with ultrasoundprobes.

The transducer portion 92 of the probe is best shown in FIG. 8. In thepreferred embodiment, the transducer portion 92 is comprised of aceramic piezoelectric crystal in the form of a hollow cylinder 94, aninside lead 96, an outside lead 98, an acoustically absorbing layer 100,an acoustically coupling layer 102, and a thin sputtered layer 104. Thehollow crystal cylinder 94 defines an inner surface 106, an outersurface 108, a proximal end 124, and a distal end 126.

In manufacturing process of the transducer portion 92, the crystalcylinder 94 if formed by extruding or molding a crystal cylinder of apredetermined length. The inner surface and the outer surface of theextruded crystal cylinder is then plated with nickel or another type ofconductive material in order to improve the conductivity between thecrystal cylinder and the leads. The extruded crystal cylinder is thencut into approximately 0.027 inches in length in order to form thecrystal cylinder 94 for the transducer portion 92.

A first end 118 of the inside lead 96 is then coupled to the innersurface 106 of the crystal cylinder with an electrically conductivematerial. Preferably, the inside lead first end 118 is coupled to thecylinder inner surface 106 by a silver conductive epoxy 110. The secondend 118A of the inside lead 96 is coupled to the probe driving circuit118B (FIG. 10) through the connector 90 in the conventional manner. Acentral portion 119 of the inside lead 96 extends through the probe body84.

The cylinder 94, with the attached inside lead 96, is then temporarilyplaced in a tube-shaped casting form or mold 142. The outside lead 98 isbent at a ninety degree angle to form an L-shape. It should be notedthat various shapes of the outside lead may function in the same manner.However, for purposes of reference, the L-shaped lead is used todescribe the preferred embodiment. The L-shaped lead is defined by along leg 112 and a short leg 114. The short leg 114 of the L-shape endsat the first end 116 of the lead 98. When the crystal cylinder 94 ispositioned in the casting form, the first end 116 of the outside lead 98is placed in close proximity to the outer surface 108 of the crystalcylinder 94, and in an imaginary plane 120 substantially tangential tothe outer surface 108 of the crystal cylinder. In this position, thelong leg 112 of the L-shaped lead 98 then extends toward the probe body84, and is located within the imaginary cylindrical shape 122 defined bythe outer surface diameter of the crystal cylinder 94. Therefore,preferably, no portion of the outside lead 98 extends outside of theboundaries of the outer diameter of the crystal cylinder 94.

The outside lead includes a central portion 138, which is the portion ofthe lead between the first and second ends. The central portion 138extends continuously along the plane of the long leg 114 of the L-shape.Thus, the central portion 138 extends through the probe body 84. Asecond end 139 (FIG. 10) of the outside lead 98 is coupled to the probedriving circuit 118B through the connector 90 in the conventionalmanner.

The layer of acoustically coupling material 102 is then depositedadjacent the distal end 126 of the cylindrical crystal 94. Theacoustically coupling layer 102 is also referred to as the matchinglayer. Preferably, an epoxy material is used for the matching layer. Theepoxy material is selected so as to be acoustically coupled with thetransducer. As shown in FIG. 8, the acoustically coupling layer 102 isformed in a plug shape, and may extend into a portion or all of thecenter of the crystal hollow cylinder.

The purpose of the acoustically coupling layer 102 is to generate asolid cone forwardly oriented ultrasound wave velocity beam 146 (shownin FIG. 9) from the transducer 92. The sound wave velocity beamgenerated by the transducer without the acoustically coupling layerresembles a first cone with a second hollow cone portion in the centerof the first cone. However, with the acoustically coupling layer, thesecond hollow cone is filled with sound waves, and the velocity beam 144becomes a solid cone. The purpose and function of the forwardly orientedsolid cone ultrasound wave velocity beam is described in more detailherein. Therefore, the acoustically coupling layer 102 allows for moreaccurate readings from the transducer.

The layer of acoustically absorbing material 100 is then depositedadjacent a proximal end 124 of the crystal cylinder. Preferably, anepoxy material doped with approximately eighteen to twenty-six percentrubber powder, such as HYCAR (™) type 1422 polymer, available from ZeonChemicals, Inc., Ill., sifted through a 100 mesh screen, is used so asto act as a sound absorber. This layer of epoxy is also known as thebacking layer of the transducer portion 92. The acoustically absorbinglayer 100 is preferably formed in a plug shape, and may extend into aportion or all of the center of the hollow crystal cylinder 94.

At this point, the transducer portion is removed from the casting form142. The matching layer, or acoustically coupling layer is then grounddown to a predetermined length, so as to enable the transducer toproduce a 1/4 or 3/4 ultrasound wave length signal.

After the matching layer 102 is ground, the sputtered layer 104 isapplied in order to make the electrical connection between the crystalcylinder outer surface 108 and the outside lead 98. The thin sputteredlayer 104 of conductive material, preferably gold or chromium, issputtered along the plane 120 defined by the crystal cylinder outersurface 108 and the outside lead first end 116. Once the layer 104 ofgold or chromium is applied, the outside lead 98 is then conductive withthe crystal cylinder outer surface 108. Therefore, when current isapplied to the leads 96, 98, current will flow from the inner surface106 of the crystal to the outer surface 108 of the crystal or viceversa. Moreover, because the outside lead 98 is not directly attached tothe outer surface 108 of the crystal cylinder, the dead spots in theultrasound wave pattern are eliminated, and the probe 82 retains itsrelatively small outer diameter.

The sputtered layer 104 in FIG. 8 is shown covering the entire outersurface of the transducer portion. However, the sputtered layer 104 onlyneeds to be applied to the plane 120 so as to electrically connect theouter surface of the crystal cylinder and the outside lead 98. Anelectrical isolation layer 140, also referred to as a conformal coating,is then deposited over the outer surface of the transducer portion. Theelectrical isolation conformal layer 140 is preferably formed of abiocompatible non-attenuating coating, such as a UV curable adhesivematerial, for example DYMAX (™) 20159 adhesive from Dymax EngineeringAdhesives, Conn.

Referring back to FIG. 7, the construction of the probe body 84 isdescribed. If desired, the probe body 84 may include a stiffener member128 that extends from the probe body proximal end 86 to the probe bodydistal end 88. The stiffener member 128 prevents kinks in the probe body84 in tight turns, as well as provides strength. The distal end 88 ofthe probe body is preferably attached to the transducer portion 92 by anadhesive layer 136.

As previously described, the second ends of the inside and outside leadcentral portions 119, 138 extend toward the probe body 84. After thestiffener member 128 is secured to the transducer portion 92 by theadhesive layer 136, the inside and outside lead central portions 119,138 are twisted and extend to the second ends of the leads, which arecoupled to the driving circuit of the probe through the connector 90.The twisting of the leads 96, 98 serves to reduce electrical noise to aminimum. A flat spring wire 132 is coiled around and surrounds thestiffener member 128 and twisted leads 96, 98.

The probe body 84 also includes a depth or zero alignment mark 134 onthe outer surface of the probe body 84 near the proximal end. The depthmark 134 is visible through the extension tubes 16 of the catheter 10.The depth mark 134 is positioned such that the mark 134 is aligned witha predetermined location on the catheter extension tube 16 when theprobe 82 is properly positioned within the catheter 10.

For purposes of reference only, the preferred dimensions of theultrasound probe 82 are given. The outer diameter of the transducer 94of the probe 82 is preferably approximately 0.040 to 0.047 inches, thewall thickness is preferably 0.010 inch, and the length is preferably0.027 inch. The outer diameter of the probe body is preferablyapproximately 0.037 inches. In comparison, the probe lumen 36 has adiameter of approximately 0.056 inches. Therefore, the probe andtransducer portion diameter is sufficiently small to allow the probe tofit within the first lumen 36 of the catheter 10, as well as to allowadditional fluid flow through the first lumen 36 if required by thecircumstances. The total length of the probe 82 is preferablyapproximately 79.75 inches. The length of the transducer portion 92 ofthe probe 82, including the matching layer and backing layer, ispreferably approximately less than 0.5 inches.

In the preferred embodiment, the ultrasound probe of the presentinvention is used in connection with a system that includes a Dopplerunit (not shown) and personal computer (not shown). The Doppler unit isused to drive the probe and to house the Doppler electronics. Thepersonal computer is used to control the Doppler unit and display andprocess the signal data. The personal computer calculates the flow areausing two components. The first component measures flow velocity and thesecond component measures flow area. The flow rate is a product of thetwo components.

Referring now to FIGS. 9 & 10, in the preferred embodiment of theultrasound probe, the single cylindrical transducer 92 instantaneouslyanalyzes the blood flow area and the blood flow velocity substantiallysimultaneously. It should be noted that the area and velocity are notmeasured precisely simultaneously in real time, but, as is known, themeasurements are made essentially simultaneously, on the order ofmillionths of seconds. More specifically, the single cylindricaltransducer 92 may be activated in two distinct modes instantaneously.

Each of the modes is activated at a different frequency. In the firstmode for producing a beam for determining the area of the pulmonaryartery for example, a frequency generator in the signal source 118B(FIG. 10) generates an 8 MHz signal in turn causing the transducer togenerate an ultrasound signal in a radial direction, thereby creating aradially oriented signal beam 146 (FIG. 9). A standard frequencygenerator such as an Hewlett-Packard signal generator may be used todrive the transducer. In the second mode, for producing a beam fordetermining the blood velocity in the pulmonary artery for example, thefrequency generator generates a 2 MHz signal in turn causing thetransducer to generate an ultrasound signal in an axial direction,thereby creating an axially directed signal beam 144 (FIG. 9). Thetransducer crystal is preferably designed such that the optimum drivingfrequency for the radially directed beam 146 is 8 MHz while the optimumdriving frequency for the axially directed beam 144 is 2.285 MHz. Morespecifically, for signal generator driving frequencies of 8 MHz and 2MHz, respectively, the presently preferred transducer crystal dimensionsare an outer diameter of 0.040-0.047 inch, a wall thickness of about0.010 inch, and a length axially of about 0.027 inch. The differencebetween the respective driving frequencies and the transducer crystaldesign dimensions results in decoupling of the two driving signals forthe preferred design. However, the transducer may be driven at otherfrequencies. When the transducer is driven at other frequencies, thetransducer design is preferably modified so as to be optimized at theother frequencies, while preferably keeping the two frequencies forwhich the transducer is designed decoupled. The different dimensions maybe determined by modeling.

The transducer crystal is preferably formed from PZT--5H, a formulationof Pb(Zr,Ti)O3 with high electromechanical coupling coefficient and highdielectric constant.

The dimensions of the crystal are also designed to generate the axiallyor forwardly directed beam 144 in the shape of a wide cone. The widerthe cone, the closer the velocity measurement is taken to the pointwhere the area measurement is taken.

The radially oriented signal beam 146 is used to calculate thecross-sectional area of the blood flow. More specifically, the flow areais estimated by measuring the Doppler power in a narrow Doppler gate ofpredetermined area, Pn, for example one centimeter squared, and thepower from a wider gate of an unknown area, Pw, which corresponds to theunknown flow cross-sectional area. The measured power from the widergate Pw corresponds to the number of red blood cells insonified withinthe Doppler gate. The corresponding number of red blood cells insonifiedis proportional to the unknown cross-sectional area Pw. Therefore, if

    Pn=1 cm.sup.2 ;

and

    Pw=x cm.sup.2

in order to calculate Pw, the unknown cross-sectional area, thefollowing equation is used:

    Pw/Pn=x cm.sup.2

In the second mode, the forwardly oriented signal beam 144 is used tocalculate the blood particle velocity. The blood velocity is calculateddirectly from the Doppler frequency shift as measured by the forwardlyoriented signal beam 144.

In order to eliminate the effect of the angle of incidence a between theaxis of the transducer and the blood flow, the following equation isused to calculate the blood flow:

    Q=V cos (a)*(A/cos(A))

wherein Q=blood flow; V=blood velocity; A=cross-sectional area; anda=angle of incidence between transducer axis and blood flow. In theequation for blood flow, the cos(a)'s cancel out, therefore eliminatingthe effect of the angle of incidence on the blood flow measurement.Because of the perpendicular nature of the radially and axially directedbeams, the estimate of the volume flow would be self-compensating orindependent of the orientation of the probe with the flow field.

By way of example, in one embodiment of the invention, the systempersonal computer screen displays the diameter mode signal echo patternin M-mode, wherein the X-axis represents time, the Y-axis representsdepth, and the Z-axis represents echo amplitude. Simultaneously, thesecond mode information, the velocity mode, is also preferably displayedin M-mode on the computer screen. Preferably the second mode display iscolor coded so as to clearly represent the speed of the moving bloodparticles.

Once the information is displayed on the screen, the user, referring tothe first mode, marks the first echo nearest the probe, and the lastDoppler signal furthest from the probe. These two measurements are usedby the computer to determine the cross-sectional area. In the secondmode, the velocity mode, the user marks the velocity wave. The meanblood flow velocity over the cardiac cycle is then calculated from thismarked information.

The blood flow velocity and cross-sectional area are then calculated,using the above equation, so as to compute the blood flow. Therefore,the use of the distinct first and second modes of the single transducerelement provide for an accurate blood flow measurement, whileeliminating the effects of the angle of incidence between the transduceraxis and the blood flow.

As previously described, the probe 82 is preferably designed for usewith the multi-lumen catheter of the present invention. In addition tothe previously described advantages of the multi-lumen catheter, thedesign of the catheter body 12 also provides the advantage of structuralintegrity. The configuration of the lumens and the thickness of thelumen walls contributes to the structural integrity and strength of thecatheter body, thereby minimizing the possibility that the catheter maybe constricted or crushed during use. More specifically, in thepreferred embodiment of the invention, a substantial portion of each ofthe lumen walls preferably has a thickness greater than the shortestdistance between the first wall of the probe lumen and the outer edge ofthe catheter body 12. Therefore, any possibility that the catheter body12 may be pressed or any lumens may be constricted when the catheter ispassed through a seal on an outer transport catheter is minimized.

Referring back to FIGS. 1-4, in a further preferred embodiment of theinvention, a transport catheter includes the probe and injectate lumens36 and 40, respectively but omits the inflation balloon and theinflation lumen. Omitting the inflation lumen allows the injectate lumento be made larger if necessary by increasing the arcuate length orarcuate extent of the injectate lumen, thereby increasing itscross-sectional area and its flow characteristics. The catheter of thisalternative preferred configuration has a number of applications,similar to those of the embodiment of FIG. 1, including sensing, fluidinjection and sampling and the like. The probe lumen is still preferablycircular in cross-section and occupies a substantial portion of thecatheter cross-section. The injectate lumen is also preferably crescentshaped and occupies as much of the remaining cross-sectional area of thecatheter as necessary to achieve high fluid flow in the lumen or toallow efficient introduction of more viscous fluids.

An alternative embodiment of a catheter 68 (FIG. 6) includes a firstlumen exit port 70 proximal of the distal end of the catheterapproximately 30 centimeters, in the embodiment where the catheterlength is 110 centimeters. A round lumen plug 74 is sealed in thecircular first lumen 76 to direct fluid from the first lumen externallyof the catheter. The port 70 allows infusion of a fluid through thefirst lumen into the body cavity at a relatively high flow rate. Thecross-sectional area of the port 70 is preferably the same as that ofthe first lumen. The cross-sectional configuration of the catheter ispreferably the same as that shown in FIG. 2 to allow the relatively highfluid flow rates in the first lumen and in the injectate lumen, whilealso having a relatively small inflation lumen 78 and a relatively smallfourth lumen. The injectate lumen 78 preferably has the samecross-sectional configuration as the preferred cross-sectionalconfiguration of the injectate lumen 40 described above with respect toFIG. 2. A portion of the bottom surface 80 of the injectate lumen isshown as though the segmented sectional view of FIG. 6 were taken offcenter. In a preferred form of the catheter, thermistor wires from thefourth lumen cross over through the wall between the first and fourthlumens. The wires extend into the first lumen near the distal end of thecatheter to a thermistor that is exposed to the outside of the catheterthrough the external wall of the first lumen.

Having thus described exemplary embodiments of the present invention, itshould be noted by those skilled in the art that the within disclosuresare exemplary only and that various other alternatives, adaptations andmodifications may be made within the scope of the invention. Thus by wayof example, but not of limitation, the position and shape of the outsidelead may be modified while still having a substantial portion of thelead within the diameter defined by the outer surface of the crystalcylinders. Also the probe body portion of the probe may be designed withdifferent materials then the stiffener member and flat spring, yet stillsatisfy the purpose and function of the probe body. Accordingly, it isto be understood that the present invention is not limited to theprecise construction as shown in the drawings and described hereinabove.

We claim:
 1. An ultrasound probe for use within a transport catheter,comprising:a probe body having a distal and a proximal end; and atransducer portion attached to the probe body distal end, the transducerportion further comprising; a piezoelectric crystal hollow cylinderhaving a distal end and a proximal end, and further defining an innersurface and an outer surface, an inside lead connected to the innersurface of the crystal cylinder, a conductive material having an innersurface and an outer surface coupled to the outer surface of the crystalcylinder and extending proximally in a plane substantially tangential tothe cylinder outer surface; and an L-shaped outside lead coupled to theinner surface of the conductive material, wherein the L-shaped outsidelead has a short portion and a long portion, wherein the short portionof the L-shape is positioned in close proximity to the proximate end ofthe crystal cylinder in the plane substantially tangential to thecylinder outer surface, such that the long portion of the L-shapeextends toward the probe body and is positioned within the cylindricalvolume defined by the crystal cylinder and extending proximally thereto.2. An ultrasound probe for use within a transport catheter in accordancewith claim 1 wherein the conductive material is a thin layer ofconductive material selected from the group of gold and chromium.
 3. Anultrasound probe for use within a transport catheter in accordance withclaim 1 further comprising a layer of acoustically coupling materialdeposited adjacent the distal end of the crystal cylinder.
 4. Anultrasound probe for use within a transport catheter in accordance withclaim 3 wherein the acoustically coupling layer is comprised of an epoxymaterial.
 5. An ultrasound probe for use within a transport catheter inaccordance with claim 1 further comprising a layer of acousticallyabsorbing material deposited adjacent the proximal end of the crystalcylinder.
 6. An ultrasound probe for use within a transport catheter inaccordance with claim 5 wherein the acoustically absorbing layer iscomprised of an epoxy material doped with approximately twenty-fivepercent rubber material.
 7. An ultrasound probe for use within atransport catheter in accordance with claim 1 further comprising aconnector coupled to the first and second leads at the probe bodyproximal end.
 8. An ultrasound probe for use within a transport catheterin accordance with claim 1 wherein the probe further comprises anelectrical isolation coating layer applied over crystal cylinder outersurface.
 9. An ultrasound probe for use within a transport catheter inaccordance with claim 1 wherein the probe body is comprised of:astiffener member extending from the probe body proximal end to the probebody distal end, wherein a central portion of the first and second leadsare twisted around the stiffener member; and a spring coiled andsurrounding the stiffener member and twisted leads.
 10. An ultrasoundprobe for use within a transport catheter in accordance with claim 9wherein the stiffener member distal end is connected to the transducerby a urethane casting layer.
 11. An ultrasound probe for use within atransport catheter in accordance with claim 1 wherein the probe bodyfurther includes a depth mark in close relation to the probe bodyproximal end, wherein the depth mark is visible when the probe isproperly positioned within the catheter.
 12. An ultrasound probe for usewithin a transport catheter in accordance with claim 1 wherein thecrystal cylinder inner and outer surfaces are plated with a conductivematerial before the leads are coupled to the cylinder.
 13. An ultrasoundprobe for use within a transport catheter in accordance with claim 1further comprising;means for providing electrical energy to thetransducer element; means for generating a radially oriented ultrasoundsignal beam at a first frequency from the transducer element; means forgenerating an axially oriented ultrasound signal beam at a secondfrequency from the transducer element; means for analyzing the radiallyoriented signal beam to calculate the cross-sectional area of the bloodvessel; means for analyzing the axially oriented signal beam tocalculate the blood flow velocity in the blood vessel; and means foranalyzing the cross-sectional area and the blood flow velocity tocalculate the blood flow rate in the blood vessel.
 14. A method ofmanufacturing an ultrasound probe comprising the steps of:forming anelongated probe body having a proximal and a distal end; providing acrystal hollow cylinder having an inner surface, an outer surface, aproximal end, and a distal end; connecting an inside lead to the innersurface of the cylinder; forming an outside lead into an L-shape havinga short portion and a long portion; applying a thin layer of conductivematerial having an inner surface and an outer surface to the outersurface of the crystal cylinder and extending proximally in a planesubstantially tangential to the cylinder outer surface; positioning theshort portion of the outside lead in close proximity to the proximal endof the crystal cylinder outer surface and coupling the short portion tothe inner surface of the conductive material in the plane substantiallytangential to the cylinder outer surface, such that the long portion ofthe L-shape extends toward the probe body and is positioned within thecylindrical volume defined by the crystal cylinder outer surface andextending proximally thereto; and connecting the probe body distal endto the crystal cylinder proximal end.
 15. A method of manufacturing anultrasound probe in accordance with claim 14 further comprising the stepof disposing the crystal cylinder within a casting layer and depositingan acoustically coupling layer adjacent the distal end of the crystalcylinder.
 16. A method of manufacturing an ultrasound probe inaccordance with claim 14 further comprising the step of disposing thecrystal cylinder within a casting layer and depositing an acousticallyabsorbing layer adjacent the proximal end of the crystal cylinder.
 17. Amethod of manufacturing an ultrasound probe in accordance with claim 14further comprising the step of plating the inner surface and the outersurface of the crystal cylinder with a conductive material beforeattaching the leads to the crystal cylinder.
 18. A method ofmanufacturing an ultrasound probe in accordance with claim 14 whereinthe step of forming the probe body further comprises the stepsof:providing a stiffener member that extends from the probe body distalend to the probe body proximal end; twisting a central portion of theinside and outside leads around the stiffener member; and surroundingthe stiffener member and twisted leads with a flat spring.
 19. A methodof manufacturing an ultrasound probe in accordance with claim 14 furthercomprising the step of marking the probe body with a depth mark in closerelation to the probe body proximal end, wherein the depth mark ispositioned such that the depth mark is visible when the probe isproperly positioned within the catheter.
 20. A method of manufacturingan ultrasound probe in accordance with claim 14 further comprising thestep of connecting the probe body to the transducer portion by aurethane casting layer.
 21. A method of manufacturing an ultrasoundprobe in accordance with claim 14 further comprising the step ofselecting the conductive material from a group consisting of gold andchromium.
 22. A catheter for accepting an ultrasound probe and otherprobes, and for introducing fluid through the catheter and into a bodycavity comprising:a catheter, the catheter comprising a catheter bodyhaving a continuous outer edge surface with a corresponding maximumouter dimension and having a proximal end and a distal end and havingwalls defining in transverse cross-section, lumens including;a firstwall defining a first lumen having a cross-sectional dimensionapproximately half the outer dimension of the catheter body; a secondwall defining a curved lumen wherein the lumen occupies at least aquarter of an arc around the catheter body; and an ultrasound probe foruse within the first lumen, the probe having a cross-sectional dimensionless than the first lumen cross-sectional dimension and including;aprobe body having a proximal end and a distal end; a transducer portionattached to the probe body distal end, the transducer portion furthercomprising; a piezoelectric crystal hollow cylinder having a proximalend and a distal end, and further defining an inner surface and an outersurface; an inside lead connected to the inner surface of the crystalcylinder; a thin layer of conductive material having an inner surfaceand an outer surface coupled to the outer surface of the crystalcylinder and extending proximally in a plane substantially tangential tothe cylinder outer surface; and an L-shaped outside lead coupled to theinner surface of the conductive material, wherein the L-shaped outsidelead has a long portion and a short portion, wherein the short portionis positioned in close proximity to the proximal end of the crystalcylinder in the plane substantially tangential to the cylinder outersurface, such that the long portion of the L-shape extends toward theprobe body and is positioned within the cylindrical volume defined bythe crystal cylinder outer surface and extending proximally thereto. 23.A catheter for accepting probes and for introducing fluid through thecatheter and the body in accordance with claim 22 wherein the transducerportion further comprises a layer of acoustically coupling materialdeposited adjacent the distal end of the crystal.
 24. A catheter foraccepting probes and for introducing fluid through the catheter and thebody in accordance with claim 23 wherein the acoustically coupling layeris comprised of an epoxy material.
 25. A catheter for accepting probesand for introducing fluid through the catheter and the body inaccordance with claim 22 wherein the transducer portion furthercomprises a layer of acoustically absorbing material deposited adjacentthe proximal end of the crystal cylinder.
 26. A catheter for acceptingprobes and for introducing fluid through the catheter and the body inaccordance with claim 25 wherein the acoustically absorbing layer iscomprised of an epoxy material doped with approximately twenty-fivepercent rubber material.
 27. A catheter for accepting probes and forintroducing fluid through the catheter and the body in accordance withclaim 22 wherein the probe body is comprised of:a stiffener memberextending from the probe body proximal end to the probe body distal end,wherein a central portion of each of the inside and outside leads aretwisted around the stiffener member; and a spring surrounding thestiffener member and twisted leads.
 28. A catheter for accepting probesand for introducing fluid through the catheter and the body inaccordance with claim 22 wherein the probe body further includes a depthmark, wherein the probe body is visible when the probe is properlypositioned within the catheter.
 29. A transducer for use in anultrasound probe comprising:a piezoelectric crystal hollow cylinderhaving a distal end and a proximal end, and further defining an innersurface and an outer surface; an inside lead having a first endconnected to the inner surface of the crystal cylinder; a thin layer ofconductive material having an inner surface and an outer surface coupledto the outer surface of the crystal cylinder and extending proximally ina plane substantially tangential to the cylinder outer surface; anoutside lead having a first end coupled to the inner surface of theconductive material, wherein the outside lead first end is positioned inclose proximity to the proximal end of the crystal cylinder in the planesubstantially tangential to the cylinder outer surface, such thatsubstantially all of the outside lead is positioned within thecylindrical volume defined by the crystal cylinder and extendingproximally thereto.
 30. A transducer for use in an ultrasound probe inaccordance with claim 29 wherein the thin layer of conductive materialis selected from the group consisting of gold and chromium.
 31. Atransducer for use in an ultrasound probe in accordance with claim 29further comprising a layer of acoustically coupling material depositedadjacent the distal end of the crystal cylinder.
 32. A transducer foruse in an ultrasound probe in accordance with claim 29 furthercomprising a layer of acoustically absorbing material deposited adjacentthe proximal end of the crystal cylinder.
 33. A transducer for use in anultrasound probe in accordance with claim 29 further comprising anelectrical isolation coating layer applied over the crystal cylinderouter surface.
 34. A transducer for use in an ultrasound probe inaccordance with claim 29 wherein the crystal cylinder inner and outersurfaces are plated with a conductive material before the leads arecoupled to the cylinder.
 35. A transducer for use in an ultrasound probein accordance with claim 29 further comprising:means for providingelectrical energy to the transducer element; means for generating aradially oriented ultrasound signal beam at a first frequency from thetransducer element; means for generating an axially oriented ultrasoundsignal beam at a second frequency from the transducer element; means foranalyzing the radially oriented signal beam to calculate thecross-sectional area of the blood vessel; means for analyzing theaxially oriented signal beam to calculate the blood flow velocity in theblood vessel; and means for analyzing the cross-sectional area and theblood flow velocity to calculate the blood flow rate in the bloodvessel.
 36. An ultrasound probe for measuring the blood flow rate in ablood vessel comprising:a single cylindrical transducer element definingan axis and a radius; means for providing electrical energy to thetransducer element; means for generating a radially oriented ultrasoundsignal beam at a first frequency from the transducer element; means forgenerating an axially oriented ultrasound signal beam at a secondfrequency from the transducer element; means for analyzing the radiallyoriented signal beam to calculate the cross-sectional area of the bloodvessel; means for analyzing the axially oriented signal beam tocalculate the blood flow velocity in the blood vessel; and means foranalyzing the cross-sectional area and the blood flow velocity tocalculate the blood flow rate in the blood vessel.
 37. An ultrasoundprobe for measuring the blood flow in a blood vessel in accordance withclaim 36 further comprising means for simultaneously generating theradially oriented and axially oriented beams from the transducerelement.
 38. An ultrasound probe for use within a transport catheter,comprising:a probe body having a distal and a proximal end; a transducerportion attached to the probe body distal end, the transducer portionfurther comprising;a piezoelectric crystal hollow cylinder having adistal end and a proximal end, and further defining an inner surface andan outer surface, an inside lead connected to the inner surface of thecrystal cylinder, a conductive material having an inner surface and anouter surface coupled to the outer surface of the crystal cylinder andextending proximally in a plane substantially tangential to the cylinderouter surface; and an L-shaped outside lead coupled to the inner surfaceof the conductive material, wherein the L-shaped outside lead has ashort portion and a long portion, wherein the short portion of theL-shape is positioned in close proximity to the proximate end of thecrystal cylinder in the plane substantially tangential to the cylinderouter surface, such that the long portion of the L-shape extends towardthe probe body and is positioned within the cylindrical volume definedby the crystal cylinder and extending proximally thereto; means forproviding electrical energy to the transducer element; means forgenerating a radially oriented ultrasound signal beam at a firstfrequency from the transducer element; means for generating an axiallyoriented ultrasound signal beam at a second frequency from thetransducer element; means for analyzing the radially oriented signalbeam to calculate the cross-sectional area of the blood vessel; meansfor analyzing the axially oriented signal beam to calculate the bloodflow velocity in the blood vessel; and means for analyzing thecross-sectional area and the blood flow velocity to calculate the bloodflow rate in the blood vessel.
 39. A transducer for use in an ultrasoundprobe comprising:a piezoelectric crystal hollow cylinder having a distalend and a proximal end, and further defining an inner surface and anouter surface; an inside lead having a first end connected to the innersurface of the crystal cylinder; a thin layer of conductive materialhaving an inner surface and an outer surface coupled to the outersurface of the crystal cylinder and extending proximally in a planesubstantially tangential to the cylinder outer surface; an outside leadhaving a first end coupled to the inner surface of the conductivematerial, wherein the outside lead first end is positioned in closeproximity to the proximal end of the crystal cylinder in the planesubstantially tangential to the cylinder outer surface, such thatsubstantially all of the outside lead is positioned within thecylindrical volume defined by the crystal cylinder and extendingproximally thereto; means for providing electrical energy to thetransducer element; means for generating a radially oriented ultrasoundsignal beam at a first frequency from the transducer element; means forgenerating an axially oriented ultrasound signal beam at a secondfrequency from the transducer element; means for analyzing the radiallyoriented signal beam to calculate the cross-sectional area of the bloodvessel; means for analyzing the axially oriented signal beam tocalculate the blood flow velocity in the blood vessel; and means foranalyzing the cross-sectional area and the blood flow velocity tocalculate the blood flow rate in the blood vessel.